Fine mapping of qAHPS07 and functional studies of AhRUVBL2 controlling pod size in peanut (Arachis hypogaea L.)

Systematic investigation and validation of peanut genetic transformation via the pollen tube injection method

Genetic transformation is a pivotal approach in plant genetic engineering. Peanut (Arachis hypogaea L.) is an important oil and cash crop, but the stable genetic transformation of peanut is still difficult and inefficient. Recently, the pollen tube injection pathway has been shown to be effective for the genetic transformation of peanut. However, the poor reproducibility of this pathway is still controversial. In this study, the appropriate time and location of injection, along with transgenic screening, were systematically investigated in the pollen tube mediated peanut genetic transformation. Our findings revealed that Agrobacterium injections could be conducted within a time window of two to three hours preceding and succeeding the blooming process. Among the various selective markers evaluated, the Basta screening emerged as the most expedient, followed closely by the DsRed visual screening. According to resistance screening and molecular identification, the average transformation efficiency was 2.6% in the heritable transgenic progenies, which was more likely affected by individual operation by style cavity injection. Furthermore, the use of synergistic FT artificially regulated the blooming of peanuts under indoor conditions, facilitating operations involving keel petal injection and ultimately enhancing the genetic transformation efficiency. Thus, our study systematically validated the feasibility of peanut genetic transformation through an optimized pollen-tube injection technique without tissue culture, potentially guiding future advancements in peanut engineering and molecular breeding programs.

Co-localization of quantitative trait loci for pod and kernel traits and development of molecular marker for kernel weight on chromosome Arahy05 in peanut (Arachis hypogaea L.)

KEY MESSAGE

Stable QTL for pod and kernel traits were co-localized on chromosome Arahy05, and an INDEL marker at 106,411,957 on Arahy05 was developed and validated to be useful for marker-assisted selection of kernel weight. Pod and kernel traits, such as hundred pod weight (HPW), and hundred kernel weight (HKW), along with pod and kernel sizes, are pivotal determinants of yield in peanut breeding programs. This study sought to identify quantitative trait loci (QTL) that are associated with these pod and kernel traits in peanuts. To achieve this, a recombinant inbred line (RIL) population, was derived from a cross between Yuhua15, a cultivar known for its high yield, and a germplasm accession W1202. The investigation uncovered stable and major QTL that are significantly associated with both pod and kernel weight and were consistently co-localized on chromosomes Arahy05 and Arahy08. Furthermore, an INDEL marker was identified and characterized in the QTL interval on Arahy05. An extensive re-sequencing analysis comprising 395 germplasm accessions led to the discovery of two principal haplotypes within a 500-kb window flanking the aforementioned INDEL marker. The haplotypes exhibited a significant correlation with the HKW in our diverse panel of germplasm accessions. Notably, the 170 accessions harboring the haplotype associated with an increased HKW primarily represented botanical varieties, specifically Arachis hypogaea var. hypogaea and A. hypogaea var. hirsuta. On the other hand, the 137 accessions associated with the alternative haplotype, which corresponded to a reduced HKW, were predominately identified as belonging to botanical varieties within A. hypogaea subsp. fastigiata. The INDEL marker located on Arahy05, which demonstrates close linkage to the pod and kernel traits, would be an efficient approach for marker-assisted selection (MAS) of pod and kernel weight in breeding programs.

Identification of candidate genes associated with peanut pod length by combined analysis of QTL-seq and RNA-seq

Pod length (PL) is one of the major traits determining pod size and yield of peanut. Discovering the quantitative trait loci (QTL) and identifying candidate genes associated with PL are essential for breeding high-yield peanut. In this study, quantitative trait loci sequencing (QTL-seq) was performed using the F2 population constructed by a short-pod variety Tifrunner (Tif) and a long-pod line Lps, and a 0.77 Mb genomic region on chromosome 07 was identified as the candidate region for PL. Then, the candidate region was narrowed to a 265.93 kb region by traditional QTL approach. RNA-seq analysis showed that there were four differentially expressed genes (DEGs) in the candidate region, among which Arahy.PF2L6F (AhCDC48) and Arahy.P4LK2T (AhTAA1) were speculated to be PL-related candidate genes. These results were informative for the elucidation of the underlying regulatory mechanism in peanut pod length and would facilitate further identification of valuable target genes.

Genome-wide identification of SWEET genes reveals their roles during seed development in peanuts

Sugar Will Eventually be Exported Transporter (SWEET) proteins are highly conserved in various organisms and play crucial roles in sugar transport processes. However, SWEET proteins in peanuts, an essential leguminous crop worldwide, remain lacking in systematic characterization. Here, we identified 94 SWEET genes encoding the conservative MtN3/saliva domains in three peanut species, including 47 in Arachis hypogea, 23 in Arachis duranensis, and 24 in Arachis ipaensis. We observed significant variations in the exon-intron structure of these genes, while the motifs and domain structures remained highly conserved. Phylogenetic analysis enabled us to categorize the predicted 286 SWEET proteins from eleven species into seven distinct groups. Whole genome duplication/segment duplication and tandem duplication were the primary mechanisms contributing to the expansion of the total number of SWEET genes. In addition, an investigation of cis-elements in the potential promoter regions and expression profiles across 22 samples uncovered the diverse expression patterns of AhSWEET genes in peanuts. AhSWEET24, with the highest expression level in seeds from A. hypogaea Tifrunner, was observed to be localized on both the plasma membrane and endoplasmic reticulum membrane. Moreover, qRT-PCR results suggested that twelve seed-expressed AhSWEET genes were important in the regulation of seed development across four different peanut varieties. Together, our results provide a foundational basis for future investigations into the functions of SWEET genes in peanuts, especially in the process of seed development.

Designing future peanut: the power of genomics-assisted breeding

KEY MESSAGE

Integrating GAB methods with high-throughput phenotyping, genome editing, and speed breeding hold great potential in designing future smart peanut cultivars to meet market and food supply demands. Cultivated peanut (Arachis hypogaea L.), a legume crop greatly valued for its nourishing food, cooking oil, and fodder, is extensively grown worldwide. Despite decades of classical breeding efforts, the actual on-farm yield of peanut remains below its potential productivity due to the complicated interplay of genotype, environment, and management factors, as well as their intricate interactions. Integrating modern genomics tools into crop breeding is necessary to fast-track breeding efficiency and rapid progress. When combined with speed breeding methods, this integration can substantially accelerate the breeding process, leading to faster access of improved varieties to farmers. Availability of high-quality reference genomes for wild diploid progenitors and cultivated peanuts has accelerated the process of gene/quantitative locus discovery, developing markers and genotyping assays as well as a few molecular breeding products with improved resistance and oil quality. The use of new breeding tools, e.g., genomic selection, haplotype-based breeding, speed breeding, high-throughput phenotyping, and genome editing, is probable to boost genetic gains in peanut. Moreover, renewed attention to efficient selection and exploitation of targeted genetic resources is also needed to design high-quality and high-yielding peanut cultivars with main adaptation attributes. In this context, the combination of genomics-assisted breeding (GAB), genome editing, and speed breeding hold great potential in designing future improved peanut cultivars to meet market and food supply demands.

Identification of two major QTLs for pod shell thickness in peanut (Arachis hypogaea L.) using BSA-seq analysis

BACKGROUND

Pod shell thickness (PST) is an important agronomic trait of peanut because it affects the ability of shells to resist pest infestations and pathogen attacks, while also influencing the peanut shelling process. However, very few studies have explored the genetic basis of PST.

RESULTS

An F2 segregating population derived from a cross between the thick-shelled cultivar Yueyou 18 (YY18) and the thin-shelled cultivar Weihua 8 (WH8) was used to identify the quantitative trait loci (QTLs) for PST. On the basis of a bulked segregant analysis sequencing (BSA-seq), four QTLs were preliminarily mapped to chromosomes 3, 8, 13, and 18. Using the genome resequencing data of YY18 and WH8, 22 kompetitive allele-specific PCR (KASP) markers were designed for the genotyping of the F2 population. Two major QTLs (qPSTA08 and qPSTA18) were identified and finely mapped, with qPSTA08 detected on chromosome 8 (0.69-Mb physical genomic region) and qPSTA18 detected on chromosome 18 (0.15-Mb physical genomic region). Moreover, qPSTA08 and qPSTA18 explained 31.1-32.3% and 16.7-16.8% of the phenotypic variation, respectively. Fifteen genes were detected in the two candidate regions, including three genes with nonsynonymous mutations in the exon region. Two molecular markers (Tif2_A08_31713024 and Tif2_A18_7198124) that were developed for the two major QTL regions effectively distinguished between thick-shelled and thin-shelled materials. Subsequently, the two markers were validated in four F2:3 lines selected.

CONCLUSIONS

The QTLs identified and molecular markers developed in this study may lay the foundation for breeding cultivars with a shell thickness suitable for mechanized peanut shelling.

Identification of QTL for kernel weight and size and analysis of the pentatricopeptide repeat (PPR) gene family in cultivated peanut (Arachis hypogaea L.)

Peanut (Arachis hypogaea L.) is an important oilseed crop worldwide. Improving its yield is crucial for sustainable peanut production to meet increasing food and industrial requirements. Deciphering the genetic control underlying peanut kernel weight and size, which are essential components of peanut yield, would facilitate high-yield breeding. A high-density single nucleotide polymorphism (SNP)-based linkage map was constructed using a recombinant inbred lines (RIL) population derived from a cross between the variety Yuanza9102 and a germplasm accession wt09-0023. Kernel weight and size quantitative trait loci (QTLs) were co-localized to a 0.16 Mb interval on Arahy07 using inclusive composite interval mapping (ICIM). Analysis of SNP, and Insertion or Deletion (INDEL) markers in the QTL interval revealed a gene encoding a pentatricopeptide repeat (PPR) superfamily protein as a candidate closely linked with kernel weight and size in cultivated peanut. Examination of the PPR gene family indicated a high degree of collinearity of PPR genes between A. hypogaea and its diploid progenitors, Arachis duranensis and Arachis ipaensis. The candidate PPR gene, Arahy.JX1V6X, displayed a constitutive expression pattern in developing seeds. These findings lay a foundation for further fine mapping of QTLs related to kernel weight and size, as well as validation of candidate genes in cultivated peanut.